Barcelona lost for the first time this season as quickfire goals from Nabil El Zhar and Oscar Rodriguez saw Leganes move off the foot of the La Liga table with a shock 2-1 victory.
Leganes had taken only one point from their opening five matches and would have sensed a fruitless night lay ahead when the defending champions took a 12th-minute lead through Philippe Coutinho.
However, a Barca line-up also containing Lionel Messi, Ousmane Dembele, Ivan Rakitic and Gerard Pique were stunned as El Zhar drew the hosts level before Oscar struck almost immediately afterwards.
Barca, who had scored eight times in their previous two trips to the Estadio Municipal de Butarque, predictably threw everything forward in search of a leveller to no avail.
They had dropped points for the first time in this campaign following a pulsating 2-2 draw at home to Girona on Sunday but this is a chastening defeat compounded by Real Madrid loanee Oscar bagging the clincher.
Real Madrid conceded three-first half goals in a 3-0 loss at Sevilla on Wednesday, squandering a chance to go top of La Liga after Barcelona lost 2-1 at bottom side Leganes.
Portugal forward Andre Silva scored two in five minutes, and Wissam Ben Yedder added another in the 39th minute to seal Sevilla’s convincing win at Ramon Sanchez-Pizjuan Stadium.
The result leaves Madrid and Barcelona level with 13 points after six matches. Madrid’s only previous setback in the league had been a draw at Athletic Bilbao on matchday four.
Luka Modric scored for Madrid early in the second half but the goal was disallowed after VAR showed he was offside.
Marcelo appeared to injure a muscle midway through the second half but coach Julen Lopetegui couldn’t replace him because he had already made all three substitutions.
Sevilla have won three in a row in all competitions, outscoring opponents 14-3. It moved three points behind Madrid and Barcelona in the league.
Silva, signed by Sevilla in the offseason, is La Liga’s top scorer with six goals from as many matches.